Conventionally, an electric heater for a batch type heat-treating equipment for semiconductor wafers is known, such as one employing a metal resistance heating element (cf. Japanese Patent Unexamined Publication No. 2001-267261 bulletin), and another employing a non-metal resistance heating element (cf. Japanese Patent Bulletin No. 3307924).
A heating element as described in Japanese Patent Unexamined Publication No. 2001-267261 bulletin employs, as a metal wire, a Kanthal (brand name) wire made of iron/chrome/aluminum system or a similar material, of around 1–3 mm wire diameter called “light gauge”. Besides, a heating element which employs a Kanthal wire or a similar material, of around 7–10 mm wire diameter called “heavy gauge” is used. In case of a heater which employs either of a Kanthal wire and its equivalents as a material of a heating element, the temperature of the heating element can reach 1250–1300 degrees Celsius at maximum when the heater temperature is 1200 degrees Celsius; and because the heating element starts to creep and is susceptible to damage at temperatures of above 1200 degrees Celsius, the set temperature of the heat treating equipment employing this type of heating element is limited to temperatures not higher than 1200 degrees Celsius or so. Additionally, at one end zone of a heater, for example, at the bottom zone of a vertical furnace, unfavorable thermal insulation condition due to charging, discharging of the work, and existence of moving section can cause increased loading; so that a problem with such a zone has been that deformation and/or breaking of a metal resistance heating element can occur more frequently.
Then, employing a non-metal resistance heating element as described in the Japanese Patent Bulletin No.3307924 would enable an application of a heater at higher temperatures compared with a heater which employs a metal resistance heating element; however, because a non-metal resistance heating element is expensive, fragile and easy to break, a problem with such a heating element has been that not only its initial cost but also repair cost on failure are high.
In view of the above-mentioned fact, the purpose of the present invention is to provide an electric heater for semiconductor processing equipments which is inexpensive and usable without problems even at high temperature.